1. Field of the Invention
The invention relates to exhaust manifold devices.
2. Description of the Related Art
The invention relates more particular to devices that are arranged to automatically allow air to enter the exhaust manifold to prevent inter alia exhaust gases being sucked into engine cylinders during the normal operation of the engine. Such devices or aspirators have been disclosed already in, for example, U.S. Pat. No. 3,455,106 and European Patent 0041831. Devices so far proposed comprise relatively complicated mechanical arrangements and do not operate efficiency at higher engine speeds or at a variety of engine speeds.
It is an object of the invention to overcome or at least reduce these problems,
According to the invention there is provided an aspirator for allowing air automatically to selectively enter an engine exhaust manifold during operation of an internal combustion engine to inhibit exhaust gases being drawn back into the cylinders via exhaust valves, the aspirator comprising an adapter that fits to the manifold having a port in communication with the manifold, a first one way valve fitted to the adapter that prevents gases leaving the manifold through the port when the pressure inside the manifold is greater than the pressure at the first valve, and a second one way valve connected by a passageway to the first valve, the second one way valve being arranged to allow air to enter the passageway whenever the pressure inside the passageway is less than the pressure at the second valve; and means for supplying air to the second valve at different pressures, above atmospheric pressure, that increase with increases of speed of the engine.
The aspirator may comprise a hollow body that extends to the port fitted to the manifold and the port be formed in a tube that extends somewhat in to the manifold beyond its inner surface.
The hollow body may be formed with an intermediate expansion chamber.
The one way valves may each comprise a needle valve.
The passageway is preferably formed with an intermediate expansion chamber.
The position of the second one way valve may be manually adjustable to vary the differential pressure at which the second valve opens and closes.
The air may be supplied to the second one way valve by an air ram having an inlet exposed forwardly in a vehicle in which the engine is mounted so as to provide air at a pressure corresponding to the forward speed of the vehicle.
The air may also or alternatively be supplied by an air pump, and the air pump may form part of a turbo charger for the engine.
An exhaust manifold device or aspirator according to the invention will now be described by way of example with reference to the accompanying schematic drawings in which: